Apparatus for and process of separating or extracting cellulose or paper pulp



June 3, 1930. E. SPENCER APPARATUS FOR AND PROCESS OF SEPARATING OR EXTRACTING CELLULOSE OR PAPER PULP Filed Feb. 10,

Patented June 3, 1930 umra STATES PATENT OFFICE APPARATUS FOR AN D PROCESS OF SEPARATING OR EXTRACTING CELLULOSE R PAPER PULP Application filed February 10, 1928, Serial No. 253,310, and in British India H9128, 1927.

This invention relates to improvements in the'separation or extraction of cellulose or paper-pulp from bamboo, wood, grasses, reeds or other suitable fibre yielding vegetable material by processes involving the treatment of the said materials with caustic or other digesting liquors in digesters.

The invention relates mainly to apparatus for carrying out improved processes of separation or extraction of cellulose. It is more particularly applicable to providing apparatus for carrying out the processes claimed in Patent No. 1,690,954,'dated November 6,1928, but it is not limited to apparatus for carrying 5 out such processes alone owin to the applicability of the apparatus (which will be de-' scribed in detail hereinafterlto other processes and to developments and modifications of the said processes.

Certain modifications and developments of the said process are also included within the scope of the claims appended hereto.

This invention comprises apparatus for the semi-continuous extraction or separation of cellulose or paper pulp from bamboo, grasses;

' wood, reeds or other fibre-yielding vegetable material adapted to work on a digestion process on the cascade or pro essive system, such for example as any 0 these processes claimed in the above mentioned Patent No. 1,690,954 or a processes set forth hereinafter, wherein the digesters are linked up in a ring or closed circuit adapted to work on a prin-.

turn into each digester inthe ringand the.

stock in any one digester is subjected therein successively to a series of treatments with caustic or other liquor in successively inreas- I ing active chemical concentrations each treatment being at a higher pressureland temperature than the last until the digestion is complete, and the stock or lpulp, still in the same digester, is subsequent y leached preferably first with used and heated leac in liquor which has been used at least once be ore, and finally with one or more washes of water, the digester being then unloaded of its ulp and reloaded with a fresh charge of cellu ose conciple analogous to that known in the chemical taining stock, characterized in that the caustic or other digesting liquor used in the digestion in any one digester with such non-cellulosic matter dissolved out and carried by the same is passed from that digester to the nextbut one digester in operative sequence under digestion in the cycle working at a lower pressure and free causticor digestion liquor concentration.

In this apparatus the digesters are connected in a ring or closed circuit having ring pipe or trunk connections and the necessary cocks and valves, whereby the liquor in any one digester may be transferred to any other digester in the ring, andfd'rther connections are provided whereby any digester in the ring may be supplied with steam, wash water or digesting liquor and whereby the spent liquors may be drawn 01f.

In the preferred embodiment the digesters are connected up in a double ring, and two ring pipes or trunks for transferring digester liquo t, make up li nor or wash water to and from the digestion in the double ring are provided, characterized by alternate digesters in the double ring being connected to alternate ring pipes by suitable valves and cocks so arranged that the alternate digesters may be operated independently in their closed rin circuits, suitable steam, liquor and was% water or the like connections being provided and connections for drawing olf spent liquors.

Whereas two rings may be provided for digesting liquor and wash or make-up water only a single live-steam ring pipe and a single spent-liquor-discharge ring pipe need be provided with connections from the last two ring pipes to all the digesters,

The apparatus also may include the feature according to which connection from the wash water-tanks are made to both liquor transferring rings with cocks, preferably pumps also, controlling the supply, and wherein separate tanks are provided similarly connected to both such rin s for receiving the first wash water and t e second or subsequent, wash water respectively, the arrangement being such that wash water which has been used at least once for wash- 100 mg out or leaching the contents of a digester (t e digestion in which is completed and which has been partially washed already) may, after use in the primary or an early washing of the next digester the digestion in which is finished, be transferred or pumped into the tank for receiving the second or several-times-used wash-water, connections being provided whereby the said wash-water from the last mentioned tank may be pumped or transferred as a primary wash to another digester the digestion in which is subsequently finished, or be used as make-up liquor in any of the digesters in the system.

In the apparatus according to this invention the arrangements may be such that, whilst the digestion is arranged to be carried out in steps or stages the pressure and or the free caustic or active liquor concentration being increased or modified progressively in each successive step or stage, the transfer of or the blowing down of digestion liquor from one digester to another in the digestion may take place simultaneously with a similar operation carried on between two other digesters, which second pair are in the alternate ring and in an overlapping stage of their di estion process.

loreover, the apparatus may be so arranged or modified that economy in time and in labour and in the continuous utilization of the services of the staff ma be effected by the simultaneous transfer or blowing over of liquors between two pairs (or more than two pairs, if the plant is sutficiently extensive and suitably arranged) of digesters at atime,

owing to the processes being made to over-lap each other by sufiicient amounts to allow the said'stafi to make all the necessary connection for the operation between any pair of digesters, and, whilst said operation is in pro ess, turn their attention to the making of t e necessary connections for the operation between a second pair (or other pairs) of di esters.

he invention also includes within its scope a process of semi-continuous extraction or separation by digestion of cellulose or paper pulp from material containing the same, which is adapted to be carried out in apparatus as herein explained, or is a modification of the kinds of processes such as are claimed in the previously mentioned Patent No. 1,690,95i but is characterizedby the feature that, the digesters being linked up in two rings, or in a double ring alternate digesters ing ada ted to be connected to alternate rings for t e purposes of being blown over, a method of operation is available wherein, owing to the said two or double ring system being used, two digesters connected to one ring may be transferring the liquor or liquid contents one to the other simultaneously as two digesters in the other ring are similarly operating, whereby a saving of time may be eflected and the loading and unload- I ing of the digesters be facilitated.

The invention also includes such a process but wherein two pairs of digesters are simultaneously transferring their liquid contents one to the other, or wherein at least one pair is being operated in this manner and another digester is simultaneously discharging its spent liquors to the recovery plant or other desired destination, characterized by the feature that the transfers of the said liquid contents are over-lapped by sufficient amount to allow the staff to make all the necessary arrangements or connections for the one transfer to start or for that transfer to take place in over-lapped relation to the start or the carrying out of the other transfer, said second transfer being in its turn over-lapped with a third transfer, and so on, for the purpose of utilizing the time and service of the staff to the greatest efiiciency.

-A preferred form the apparatus may take is described with reference to the accompanying drawings in which Fig. 1 is a diagram of a typical battery adapted to Work in a ring or closed continuous circuit on the cascade principle.

Fig. 2 is a detail of the connections.

This system is shown employing a stepdown pressure arrangement with an alternate ring series from the highest pressure digesters containing the strongest free caustic liquor and almost completely leached stockto the lowest pressure digesters with spent liquor and newly charged stock.

Figure 1 illustrates diagrammatically the arrangement with eight digesters in the cascade system Nos. 123 8 being the digesters with alternate ring pipe connections to ring mains R and R Digesters Nos. 1, 3, 5 and 7 are connected to ring R ghilst Nos. 2, 4, (i and 8 are connected to ring Digester N0. 1 is starting with bamboo or other fibrous material on its last stage of digestion under full pressure and with fresh strong caustic or other suitable digesting liquor supplied from the caustic or liquor.

tank C.

We will assume that 20% of the digestible material is removed at each stage of the diestion and that the last 20% still remains to e removed at the commencement of full pressure digestion in No. 1.

. Similarly the material in digesters Nos. 2, 3, 4 and 5, is at the same time under extraction, No. 5 being at the lowest pressure and extracting the first 20% of digestible matter. No. 4 is under a higher pressure than No. 5 and is removing the second 20%, and so on.

When digestion in No. 1 is complete di gester No. 2 is ready for its last extraction with clean fresh caustic. No. 3 digester is ready for its last-but-one digestion with only once used liquor i. e. with liquor from N o. 1.

Similarly No. 4 is ready for liquor from No. takes spent liquor from the first extraction to 2 and No. 5 for liquor from No. 3. No. 6 has the recovery plant via an eoonomizer if dein themean time been loaded with fresh stock. sired. The steam pipe ring R4 supplies To operate the cycle between No.4 and No. steam to the digesters as required to keep 6 the ring cocks 1 and 2 are opened and the them up to their respective digestion presliquor is blown over from No. 4 to No. 6. sures. Let us assume that the process in This is done by utilizing the pressure in N 0. working on bamboo and that the final diges- 4 which is considerably higher than the tion in No. 1 digester has been carried'out pressure in No. 6 which latter will generally at 100 lbs. pressure (170 0.). N o. 3 digestbe open to atmosphere -for the greater part er has finished its third or last-but-two digest of his step in the process. At the same time at lbs. pressure (153 C.) and has blown the waste cock 4 of No. 5 is opened and the its liquor over to N o. 5. The residual presliquor contained therein is blown out, using sure in the digester No. 3 is say 25 lbs. the residual pressure in No. 5, to the recovery (130 (1.). No. 1 liquor is blown into it with through pipe 6. When the digester liquors the result that the pressure in No. 1 drops have been completely blown over from Nos. 4 say to 60 lbs. and that in No. 3 rises to 50 lbs. and 5 digesters the ring cock 1 of No. 6and (148 C.). After closing No. 3 live steam the waste liquor cock 4 of No. 5 are closed, but is introduced from steam ring R through ring cock 2 is still left open, and ring cocks cock 16 into No. 3 digester by opening this 7, 8 and 9 of Nos. 2 and 3 and 5 are opened and steam cock sufliciently long to bring the presthe liquors blown over from Nos. 2 and 3 to sure up to the desired amount viz., 80 lbs. Nos. 4 and 5 respectively. Cocks 1 and 9 of (162 C.) and additional steam is supplied Nos. 4 and 5 are then closed and the ring if desired to keep up this pressure over the cock 10 of No. 1 is opened and its liquor extraction period, ng. Cock 8 still r m ining 0 is blown With a residual pressure of 60 lbs. in No.1 over to No. 3 along with some make-up wash when its digestion is complete it is necessary liquor from the wash-water tank W2 by opento pum the wash-water already used once ing the corresponding wash-water cock 11. before rom tank W1 into No. 1. Make-up liquor can also be added in the same After the first wash of No. 1 the wash-water way to digesters Nos. '4 and 5 if necessary, to (already used twice) is pumped or transaccommodate or completely cover the greater ferred into tank W2 to be used as make up volume of the less digested stock. 5 liquor for other tanks such as No.4 being al- At the same time fresh heated caustic 1s ready mixed with the digestin reagentsrepumped or blown under ressure into dicovered from Nos. 8 and 1 an heated up to gester No. 2 from the caustic tank C through a. considerabl te t,

pump 19 and cocks 12. and 7 No. 1 di gester No. 1 will have now dropped in pressure is now ready for its first wash. TlllS is also considerably and its second wash will take pumpedunder pressure through pump 20, place with water from water tank W this cocks 13 and 10 from the wash-tank W1 water being pumped into or transferred to which contains the second wash or the first No. 1 which now has really become No. 8 as water-wash of No. 8. This washis then sent the digesters numbers change in rotation as irom No. 1 digester to tank W2 thorugh cooks the process proceeds.

10 and 11 to be used subsequently as make-up The wash-water after the second wash of for No. 4 etc. No. 1 digester then receives its No. 1 (nowNo. 8) i tr f d t t k W1 second wash or first water wash. The water but has little pressure. It is however heated is umped from tank W through pump 14,- up in the process of washing and adds to and cooks 15 and 10 and this wash liquor is the heat economy of the system. sent totank W1 in readiness for the first Little heat is really lost in the process of wash of No; 2. The contents of digester No. washing and the greater part of the heat after 1 are now partly cooled owing to a good part the'final digestion is complete is recovered in of 'the heat locked up in the pulp having this process.

been extracted by the wash water sent onto It is of course understood that the prestanks W2 and VVl' respectively, the heatlng sures indicated above for'bamboo may themof which water addsto the economy of the selves be widely varied and are only given system in that it reduces the call. for live by way of illustration and may be modified steam for make-up purposes in digester No. to suit the optimum conditions for the par- 3 etc. the contents ofthe digester are flushed with digestion and for the kind of .digester liquor water and finally unloaded.

No. 8 has been unloaded and No. 7 loaded in the meantime in readiness for the next cycleof operations.

The two outer pipe rings R3 and R4 represent the recovery pi e and thesteam' pipe rings respectively; he recovery pipe 6 used.

In the above description of the operation of a cycle, it has been assumed for simplicit that the connection .to the digesters from t e alternate ring pipe systems R1 and R2 was made to the ottom of each digester via a singlevalve. Thus in blowing over a di- The drain cock D is then opened and ticular kind of fibrous material undergoing gester the liquor would pass from the bottom of the one digester to the bottom of the other.

In actual practice and if using the Sinclair type of digesters (which is one having internal vomit pipes) the blow over would be more effective if made to proceed from the bottom of the blowing off digester to the top of the receiving digester.

This result readily is obtained by means of a branch connexion from the ring pipe sys tem R1 or R2 to the top and bottom of each digester, with a valve 17 and 18, in each branch as shown in Figure 2.

. If digester A (Fig. 2) for example is blowing liquor over to another digester the lower cock 18 would be opened to the pipe ring R1 (or R2 as the case might be) and the upper one 17 closed, while if receiving liquor from another digester, the upper cock 17 would be 0 ened and the lower one 18 closed.

It may e desirable to precede the treatment of the stock with caustic by a treatment with boiling water, because by such prior treatment caustic may be econoinized owing to said hot water dissolving out the watersoluble constituents in the stock which would otherwise consume a portion of the digesting reagent. In this cascade system this preliminary washing is easily efi'ected as will readily be apparent. All that is necessary is to concentrate the washing, unloading and loading operations in digesters Nos. 8 and 7 instead of in three digesters, so that No. 6 is then available for a preliminary treatment with hot water to dissolve out the water-soluble constituents before it receives its first charge of nearly spent caustic liquors from No. 4. The water for washing out No. 6 may be obtained from wash-water tanks W1 and lVil and would thus be more or less heated already. More water and further wash water tanks would in that case be used in washing Nos. 1 and 8 than otherwise in order to supply extra water in these two tanks lVl and W2 not only for use as make-up liquor for digesters Nos. 3, 4 and 5 but also to supply the water for No. 6. The water for the preliminary treatment of digester No. 6 might however be supplied from tank W or from other source, and the same be heated up to the required temperature in No. 6 by admitting live steam through cock 21 from the steam ring R4.

From the above description of the process and a consideration of the diagram, it will be evident that the double ring cascade system of extraction can be arranged with any even number of digester-s from four upwards. In most plants eight or ten digester-s will be the preferred number. T

The proportional number of digesters under extraction outof the total number in the cascade system can also be varied from two or three upwards, as may be found necessary to meet the requirements of the particular material to be digested.

Similarly, the number of digesters in the washing, unloading, and loading and preliminary treatment-With-water sections of the cascade system can be regulated to suit the conditions of the particular operation in each case. The desideratum will be that any particular operation in the cycle should not be responsible for a hold-up in the continuous uninterrupted operation of the system. Thus, with hydraulic or other mechanical methods of unloading, one digester in the unloading section of the'system would probably be sufiicient; whereas with hand unloading and the prolonged cooling period which would be necessary, two, or even three digesters might be required in the cooling and unloading section of the system.

For some types of fibre such as bamboo it may also be found advantageous to lay more stress on the preliminary treatments and to give the raw material both a preliminary hot Water wash or/and a boil with very weak alkali solution. The insertion of one or more digesters in the cycle between the loading digester No. 6 and the 1st extraction digester No. 5 (using liquor) would provide for this and the earlier washes from the finished digester No. 1 could be collected for a weak alkali boil, it this was found to bev necessary, whilst the water from the last wash of all in No. 8 might be used for the preliminary hot water extraction.

It will be noted that a great saving of time and saving in the utilization of the services of the staff may be effected by using this plant.

Digestion may be proceeding practically continuously in the five or other number of stages selected.

In the ordinary systems of working there is great delay and part of the staff may be largely unoccupied whilst digestion is proceeding and only become really active when a digester is being blown down or refilled. According to this plant and process the ring connections R1 R2 are readily made and the rings and valves may be of large size so that it may take say only five or ten minutes to blow out the liquor from a large digester, and another five or ten minutes say, to blow in stronger-liquor and raisethe pressure to a desired level. But the connection for either of these steps having been made. the staff can then make suitable connections for a similar operation to be effected practically simultaneously but in over-lapped relation between another pair of digesters, or between two other pairs if desired, before the particular blowing over between the digester-s of the first pan is complete, thus utilizing the time of the staff fully and speeding up the operations. A considerable saving maybe effected by working in the manner suggested. For example, whilst spent liquor from N o. 5 is being run off to waste, and stronger liquor at higher pressure from No. 3 is being blown into N o. 5, simultaneously but following a little later liquor from No. 4 may be blown into No. 6 and subsequent (but over-lapping the final operation between No. 3 and No. 5) liquor from No. 2 may be blown into No. 4. Thus first No. 5 and then No. 4 (both beingdigcsters in an early stage of the digest-ionoperation and hence being in what may be termed approximately the same stage of digestion) are started on their digestion period one after the other. A similar overlapping is to be observed in the latter stages of the digestion and in the operations of the stalf in keeping the operations moving in proper sequence around the ring.

It should further be noted that another great advantage obtainable by using a double ring over that obtained by using a single ring is that the loading and unloading is made more regular when the double ring is used. This may be realized from the following Assuming the first four digesters are part of a single ring. No. 1 unloading-No. 2 loading-No. 3 on its first digest-No. 4 on its third digest. When the time is ready for Nos. 3 and 4 to blow over, the liquor in No. 3 is completely used up and goes to the recovery. The liquor in No. 4 digester, having finished the third digest of its bamboo, is blown over to No. 3 to start the second stage in the digest of the bamboo in that digester. There is no liquor ready to carry out the first digest in the freshly loaded No. 2 digester and it has to lie fallow until the second stage of digestion has been carried out in No. 3 digester. On the other hand, if there had been a double ring, the newly loaded digester would have been in the alternate ring and the digester immediately in front of it in sequence would have been undergoing its second digest, so that, the

liquor would have been blown over to the loaded digester without any delay. Of course, we might have assumed in the above four digesters that Nos. 3 and 4 were undergoing their second and fourth digests, in

which case, the liquor from No. 3 would have been blown over directly to No. 2, but this would merely push the delay forward on to No. 1 digester after it had-been loadedl In other words, with a single ring, there would be a delay after loading each alternate digester (and the same at the washing stage). This delay is avoided by using a double ring, as, what would be the delay period in each ring corresponds to the loading period in the other.

It will of course be understood that, although the invention has been described in relation to a particular lay-out of plant which has been found convenient, it is not by any means restricted in its application to the particular plant referred to, as it will be obvious that, given suitable piping, trunks, con

nections and valves, the process could be worked with very different arrangements of plant. The plant actually described moreover may be modified by introducing extra piping, tanks and pumping means if it is desired to develop the washing and preliminary treatment parts of the process.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. Apparatus for the cascade extraction of cellulose pulp from fibre yielding vegetable material comprising-a plurality of digesters, ring trunks linking up said digesters in a. closed circuit, connections between said digesters and said ring trunks whereby liquor in any one digester may be transferred to any other digester, means connected to said digesters and said ring trunks whereby any digester may be supplied with make up liquor, wash water and digesting liquor, means for supplying steam to said digesters, and means connected to said digesters whereby the spent liquor therefrom may be drawn 2. Apparatus according to claim 1, including two ring trunks for supplying digesting liquor and make-up liquor linking up the digesters in a double ring, alternate di esters being connected to the same ring trun and connections between'said digesters and said ring trunks so arranged that alternate digesters may be operated independently in their corresponding ring circuit.

3. Apparatus according to claim 1, including two ring trunks linking up the digesters in a double ring, alternate digesters being connected to the same ring trunk, connections between said digesters and said ring trunks so arranged that alternate digestors may be operated independently in their corresponding ring circuit, a steam supply ring pipe, a spent liquor discharge ring pipe, and connections between said ring pipes and each of the digestors.

4. Apparatus for the cascade extraction of cellulose pulp from fibre yielding vegetable -material, comprising a plurality of digesters,

two ring trunks for supplying digester liquor and make-up liquor linking up said digesters in a double ring, successive digestors being linked alternately to one and the other of said ring trunks, connections between said digestors and said ring trunks so arranged that alternate digesters may be operated independently in their corresponding ring circuit and liquor in any one digestor may be transferred to any other digester in the ring, a steam supply ring pipe, a spent liquor discharge ring pipe, connections between said ring pipes and each of said digesters, washwater tanks, and'connections between said tanks and said ring trunks.

5. Apparatus according to claim 4, including separate tanks for receiving the primary wash water and the secondary wash water, connections between said tanks and the ring trunks, said connections so arranged that wash water which has been used at least once as a secondary wash for a digester which has completed its digestion and been initially washed may be used as an initial wash for the next digester which has completed its digestion and thereafter transferred to said secondary wash water tank, and means connected to said secondary wash water tank for transferring said secondary wash water to one of the ring trunks for use as make-up liquor.

6. In a process for the cascade extraction of cellulose pulp from fibre yielding vegetable material, the steps of linking up a plurality of digesters in a double ring, by connecting them alternately to one and the other of two ring trunks, treating the material in said digesters in a plurality of stages the pressure and liquor concentration of which are progressively increased, and simultaneously flowing down from one to another of a pair of digesters connected to one ring trunk and from one to another of a pair of digesters connected to the other ring trunk.

7 In a process for the cascade extraction of cellulose pulp from fibre yielding material, the steps of linking up a plurality of digesters in a double ring by connecting them alternately to one and the other of two ring trunks, treating the material in said digesters in a plurality of stages the pressure and liquor concentration of which are progressively increased, the stages in the digesters connected to one ring trunk over-lapping those in the digesters connected to the other ring trunk, and simultaneously flowing down from one to another of at least one pair of digesters connected to the same ring trunk and discharging spent liquor from another digester.

In testimony whereof I hereto afiix my signature this 11th day of January, 1928.

. EDMONDSON SPENCER. 

